1. Field of the Invention
The present invention relates to a solenoid valve apparatus which opens or closes a fluid channel.
2. Related Art
Conventionally, it has been known that a solenoid valve is used as an idle-speed control valve (hereinafter, referred to as ISC valve) for controlling the flow rate of intake air flowing through an intake air bypass when an engine is idling. The solenoid valve used as the ISC valve closes the intake air bypass when a valve member as a movable member is biased by the biasing force of a spring in a direction of a valve closing position during non-excitation of a coil. On the other hand, the intake air bypass is opened when the coil is excited and electromagnetic force generated by the coil attracts the valve member against the elastic force of the spring.
In the ISC valve utilizing the solenoid valve having the structure as described above, however, if a current providing source providing current to the coil has failed or breaking of the coil or the like has occured, because the coil does not generate the electromagnetic force to attract the valve member in the direction of the valve closing position, the ISC valve remains, closing the intake air bypass. When the ISC valve closes the intake air bypass, flow rate of intake air introduced to an engine becomes zero at the time of an idling operation of the engine. As a result, there arises a problem that the engine stops. In accompaniment to the engine stop, a power steering apparatus driven by power from the engine does not operate, either. Therefore, for the sake of a fail-safe to prevent the engine stop at the time of the idling operation of the engine, even if the coil cannot be excited due to failure of the current providing source, breaking of the coil or the like, a predetermined flow rate of air must be introduced into the engine by causing the ISC valve to open.